The present invention relates to a new and improved construction of syringe for injecting liquids into blood vessels of living bodies which is of the type comprising a cylinder provided at one end with an attachment flange and at the other end with a catheter connection, a piston is introducable into the cylinder and has an elastic rubber sealing ring arranged in a groove.
In German patent publication No. 1,566,585, there is disclosed an injection device for x-ray contrast agents wherein there is taught a syringe having a to-and-fro movable piston which in conventional and therefore non-illustrated manner is provided with the required sealing ring arranged in a groove. In the assembled condition of the device such sealing ring is pressed against the inner wall of the cylinder. This seal has the drawback that due to the wall friction which prevails, upon actuation of the piston, between the deformed sealing ring and the inner wall of the cylinder and which friction only can be overcome with difficulty, there can not be guaranteed for faultless operation of the entire injection device -- piston advance speed with respect to the adjusted liquid conveying.
Furthermore, there is known to the art a syringe from German patent publication No. 2,314,949 which possesses a piston movable to-and-fro in a cylinder of the syringe, the piston having a one-piece rubber seal which surrounds the front portion of the piston first in a convex form and thereafter in a cylindrical form. The cylindrical configured portion of the seal has an inwardly directed ring-bead which engages in a groove provided at the piston and a further, but this time outwardly directed ring-bead which extends towards the inner wall of the cylinder and serves as a seal. The drawback of this syringe resides in the fact that the sealing edge formed by the ring-bead directed towards the inner wall is located at a relatively large distance from the front edge -- transition from the convex shape to the cylindrical shape -- and in this relatively narrow ring gap there are entrapped air bubbles which are difficult if not in fact impossible to eliminate. Additionally, the field of application of this syringe is markedly limited due to the rubber seal.
In German patent publication No. 2,061,802 there is taught a syringe having a piston which can move to-and-fro or reciprocate within a cylinder, this piston being provided at its front portion with a conical surface. Arranged in the piston is a mandrel provided with threading and possesses a head portion or piece provided with a conically configured surface at the side confronting the conical surface of the piston. The head portion with its conical surface is correspondingly arranged with respect to the conical surface of the piston, so that both surfaces collectively form an endless groove for a sealing O-ring held in position by a sleeve surrounding the head portion of the mandrel as well as part of the piston. By suitably rotating the mandrel in the piston both of the conical surfaces are drawn towards one another, so that the groove is reduced in size, and hence, the sealing O-ring is outwardly elongated, with the result that the sleeve at this location sealing presses against the cylinder wall. Also this syringe is associated with the disadvantage that the location serving as the seal is oriented relatively far from the front edge of the sleeve, and thus, there is formed a narrow ring-shaped gap between the cylinder wall and the sleeve within which there become entrapped air bubbles which are difficult or impossible to remove and are extremely dangerous for the patient undergoing treatment.